The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board (PCB) attached to a disk drive base of the HDA. The head disk assembly includes at least one disk (such as a magnetic disk, magneto-optical disk, or optical disk), a spindle motor for rotating the disk, and a head stack assembly (HSA). The spindle motor typically includes a rotating hub on which disks mounted and clamped, a magnet attached to the hub, and a stator. Various coils of the stator are selectively energized to form an electromagnetic field that pulls/pushes on the magnet, thereby rotating the hub. Rotation of the spindle motor hub results in rotation of the mounted disks. The printed circuit board assembly includes electronics and firmware for controlling the rotation of the spindle motor and for controlling the position of the HSA, and for providing a data transfer channel between the disk drive and its host.
The head stack assembly typically includes an actuator, at least one head gimbal assembly (HGA), and a flex cable assembly. Each HGA includes a head for reading and writing data from and to the disk. In magnetic recording applications, the head typically includes an air bearing slider and a magnetic transducer that comprises a writer and a read element. The magnetic transducer's writer may be of a longitudinal or perpendicular design, and the read element of the magnetic transducer may be inductive or magnetoresistive. In optical and magneto-optical recording applications, the head may include a mirror and an objective lens for focusing laser light on to an adjacent disk surface.
During operation of the disk drive, the actuator must rotate to position the heads adjacent desired information tracks on the disk. The actuator includes a pivot bearing cartridge to facilitate such rotational positioning. One or more actuator arms extend from the actuator body. An actuator coil is supported by the actuator body opposite the actuator arms. The actuator coil is configured to interact with one or more fixed magnets in the HDA, typically a pair, to form a voice coil motor. The printed circuit board assembly provides and controls an electrical current that passes through the actuator coil and results in a torque being applied to the actuator. A crash stop is typically provided to limit rotation of the actuator in a given direction, and a latch is typically provided to prevent rotation of the actuator when the disk dive is not in use.
The configuration of an actuator body and actuator arms is sometimes referred to as an “E-block” because its shape can resemble the letter E when viewed from the side. The distal end of each actuator arm supports at least one head gimbal assembly (HGA). The top and bottom outer actuator arms of the E-block typically each support one HGA while the inner actuator arms (if any) typically each support two HGAs. For this reason, less mass is typically coupled to the distal ends of the top and bottom outer actuator arms than to the distal ends of the inner actuator arms (if any). Such a difference in mass can adversely affect the dynamic performance of the actuator, for example exacerbating the so-called “scissor mode” and/or other modes of vibration, and/or introducing additional peaks in the frequency response function of the actuator. Some designers have attempted to alleviate the aforementioned difference in mass by adding mass to the distal ends of the top and bottom outer actuator arms, perhaps by thickening such distal ends. However, adding mass to the distal end of any actuator arm can be undesirable because it increases the rotational inertia of the actuator, and may also increase the deflection of the arm in response to mechanical shock events.
Thus, there is need in the art for an improved actuator configuration.